This invention relates to a device for checking dimensional tolerances. More particularly, the invention is a gauge for checking the circumferential length around an object at a desired location to determine if such length is within a predetermined tolerance limit.
In the manufacture of an object, certain dimensions on the object may be considered critical; that is, it may be desirable to make the article with such certain dimensions as close as possible to a specified or nominal dimension. The degree of closeness to nominal which may be attained in making the object is a function of many factors, such as the material from which the article is made, method of manufacture, costs of manufacture, etc. Regardless of the amount of variance of the dimension which may be allowed away from the nominal dimension, such variance is typically expressed as a plus or minus value away from the nominal. Thus, if the object is a cylinder or has a cylindrical portion, the outside diameter of the cylinder or cylindrical portion may be critical, and the diameter would typically be expressed as the nominal diameter "x" plus or minus a value "y". The expressed variance is termed a tolerance, and such tolerance may be applied all on the plus side away from nominal, all on the minus side away from nominal, or distributed in any way between plus or minus as the manufacturer and user of the article agree. Variance of the diameter from nominal may result in the cylinder being uniformly larger or smaller in diameter than desired, or it may result in a condition referred to as out-of-round. An out-of-round condition results if the diameter varies away from nominal nonuniformly, and such a condition may not be desirable even though the variance of the diameter away from nominal may be within the allowable diameter tolerance limits. For this reason, it is not unusual that a further tolerance is established relating to out-of-roundness, and this tolerance is typically expressed as a variance away from a mean diameter. The mean diameter is the average of the measurement of any two diameters transverse to one another.
Heretofore, manufacturers have typically checked substantially circular portions of objects for tolerance variations by taking diametrical measurements with micrometers, calipers and the like which may be time-consuming and inefficient. In many instances, even though nominal dimensions and tolerances are expressed with respect to diameters, it is the circumferential length which is critical, and it would be desirable to measure or gauge the circumferential length without the necessity of taking diametric measurements.
For example, bottles for packaging goods are often closed with a metal or plastic closure referred to as a tamper-evident closure. Typically, the closure is comprised of a cap having a top wall, a skirt depending therefrom which is adapted for selective engagement or disengagement with the bottle, and an annular band depending from the cap and connected to the skirt by frangible means. The band is adapted to engage with a portion of the bottle after the closure has been applied thereto, and when the cap is disengaged from the bottle, the frangible means fractures causing the band to separate from the cap and provide evidence that tampering with the closure has occurred. A widely used feature on a bottle to engage with a closure is a flange projecting outwardly from the bottle which locks with a portion of the band underlying the flange.
A typical tamper-evident metal closure is referred to as a roll-on closure and is adapted for assembly with a threaded bottle. The closure, as provided to the packager, is an unthreaded thin metal shell. The packager feeds the shell to a capping machine which applies the shell over the open mouth of a bottle, and rollers bear against the shell and form threads conforming to the bottle and roll the band under the bottle flange.
A typical plastic tamper-evident closure is molded substantially to its finished form and is supplied to the packager for engagement with the bottle without requiring any reforming of the closure after application. The tamper-evident band includes an inwardly projecting lug which rides over and snaps under the bottle flange as the closure is screwed onto the bottle.
If the flange of the bottle has a circumferential length greater than the inner circumferential length of the band, the closure will not assemble with the bottle unless the band is capable of stretching to the degree that the inner circumference is at least equal in length to the length of the flange circumference. This is true, whether the circumference of the flange is round or out-of-round.
In the case of a metal closure, the band cannot be stretched to effect an assembly without damaging the frangible bridges which connect the band to the cap. If a metal closure is to be used to seal a bottle, therefore, the circumferential length of the flange cannot exceed the length of the inner circumference of the band. If the closure is a plastic material, the band will stretch at least to some degree, but the fragile nature of the band and the frangible connection between the band and cap limit the amount of stretch which can be accommodated. Since closure bands, whether metal or plastic, are flexible, they can deform to pass over a bottle flange which is considerably out-of-round so long as the length of the flange does not exceed a specific limiting value. It may be seen, therefore, that a specific circumferential length of the bottle flange is the determinant as to whether an assembly between the closure and bottle can be made.
If the flange circumference were always round, variations in circumferential length could be readily determined from diametrical measurements. Such is not the case, however, if the flange is out-of-round since diameters will vary from one measuring site to another, and the length of the circumference cannot be readily determined from such measurements.
Heretofore, flanges and other portions of bottles intended to be circular have typically been checked dimensionally by measuring diameters. Such a method is time-consuming and inefficient. From the foregoing, it may be seen that it may be the circumferential lengths of one or more such portions which may be critical, rather than the diameter, and a rapid, efficient method of checking the circumferential length of bottle portions would be advantageous.